Optical Engineering

This paper demonstrates that the optical testing of diamond-turned surfaces is best accomplished by interferometry and not by tests which measure wavefront slope. Certain conditions regarding the interferometer configuration must be met in order to generate meaningful and accurate interferograms. A 40 cm diameter aperture modified Mach-Zehnder interferometer mounted directly on the diamond-turning lathe to facilitate rapid testing of figure between fabrication cuts is described. Results for a spherical surface tested in a Twyman-Green interferometer and an off-axis parabola tested in the Mach-Zehnder interferometer are illustrated.